1. Field of the Invention
The present invention relates to the automatic limiting of signals. More particularly, the present invention relates to a circuit and method for automatically limiting the amplitudes of broadcast and/or transmitted audio signals.
2. Background Art
The following figures which illustrate the various embodiments of the background art and the present invention may incorporate the same or similar elements. Therefore, where the same or similar elements occur throughout the various figures, they will be designated in the same manner.
FIG. 1 illustrates a block diagram of a known circuit for varying the amplitude of audio signals.
This figure comprises a receiving circuitry 100 and output circuitry 110 and is applicable to an analogue and/or digital system.
The receiving circuitry 100 and output circuitry could for example be the respective audio front and back ends in a radio, television, video, satellite decoder etc.
The receiving circuitry 100 receives, via an input 120, a transmitted or broadcast signal Si. The circuitry 100 then processes the signal Si and outputs, via its output 130, a first audio, i.e. sound, signal A1.
The input 140 of the output circuitry 110 is connected to the output 130 of the receiving circuitry 100 and thus the output circuitry 110 receives the signal A1. The output circuitry 110 then processes the signal A1 and outputs, via its output 150, a second audio signal A2, which is then fed to a speaker system (not illustrated).
The output circuitry 110 also receives a control signal C1 via another input 160. This control signal C1 is controlled by the user of the apparatus in which this circuitry of FIG. 1 is utilised. This signal C1 is used to control the peak, average and/or Root Mean Square (RMS) amplitude of the audio signal A2. Therefore, by increasing, for example, the RMS amplitude of the audio signal A2, the volume of the signal from the speakers is increased and vice-versa. The user can control the signal C1 by, for example, a knob or button on said apparatus or by a remote control system that works in conjunction with said apparatus.
One problem associated with the arrangement of FIG. 1 is that if there is a change in the RMS amplitude of the signal A1, then this will be proportionally reflected in the signal A2 and hence the volume. The effect of this is that the user will have to readjust the control signal C1 to return the volume emanating from the speakers, i.e. the RMS amplitude of the signal A2, to substantially the same level as before the change in the RMS amplitude of the signal A1.
An example of where changes in the RMS amplitude of the signal A1 occur are in the commercial breaks of television, satellite and radio broadcasts. During these commercial breaks quite often the amplitude of the broadcast audio signal is increased, which results in an increased volume output. The purpose underlying this increase is to stimulate the listener and draw his attention to the commercial and hence the product, service etc. being advertised. However, the increase in the level of the volume can be as much as +6 dB for example, i.e. double the amplitude of the original signal, which results in the listener diving for the control knob/button or scrabbling for the remote control device in order to reduce the volume. Then when the commercial is over, the listener has to readjust the volume back to the acceptable level it was before the commercial.
Another example of where sudden changes in the amplitude of the signal A1 occurs is during the tuning of a radio. The strengths, i.e. the amplitudes, of some signals are greater than others and it can be quite disturbing, and in some instances dangerous, when there is a sudden increase in the output volume: this is especially the case if one is tuning a car radio when driving for example.